Run ISO dialog when 'Change CD' menu is activated
    
    Also moves 'Change CD' menu item from the toplevel menu to a subitem
    under 'File' toplevel menu.
    
    In order to avoid object interdependency, it is necessary to make the
    ovirt foreign-menu pointer from RemoteViewer, accessible via property,
    so it can be passed to the dialog as an opaque GObject.
    
    Finally, with this commit, we clean up ovirt foreign menu code, which
    only deals with data, leaving the UI bits to be handled properly in the
    new ISO list dialog.
    
    Signed-off-by: Eduardo Lima (Etrunko) <etrunko@redhat.com>